This proposal addresses two fundamental questions in Neurobiology which concern the neuronal mechanisms of learning and memory on the one hand, and of development on the other. It is the goal of this research project to combine an analysis of these two questions, using each to provide insights into the other. The marine mollusc Aplysia has recently proven to be an excellent preparation for examining the neuronal mechanisms of both learning and development on a cellular level. Thus Aplysia offers a unique opportunity to combine a behavioral and cellular approach in the analysis of the development of learning and memory. In addition to its direct biological relevance, development can also provide a powerful analytic tool for studying learning and memory, for if different behavioral processes emerge sequentially, this allows one to treat the animal as a "functional mutant" examining some processes which, at least temporally, exist in the absence of others. The project will be carried out on two levels of analysis: Behavioral and Cellular. On each level, two questions will be examined: 1) Is there a temporal sequence in the emergence of different forms of learning (habitation, sensitization and classical conditioning) or memory (short-term and long-term) during development? 2) Can early experience modify the subsequent adult learning or memory capabilities of Aplysia and if so, is there a critical period during which such early experience exerts its most profound effects? Since these questions can be studied on both behavioral and cellular levels in Aplysia, it is the overall goal of this project to gain insights into the neuronal mechanisms involved in the normal development of learning and memory, and perhaps even beginning insights into mechanisms contributing to simple forms of learning disabilities.